A wireless power transmission or a wireless energy transfer refers to a technology of wirelessly transferring electric energy to desired devices. In the 1800's, an electric motor or a transformer employing the principle of electromagnetic induction has been extensively used and then a method for transmitting electrical energy by irradiating electromagnetic waves, such as radio waves or lasers, has been suggested. Actually, electrical toothbrushes or electrical razors, which are frequently used in daily life, are charged based on the principle of electromagnetic induction. Until now, the long-distance transmission using the magnetic induction, the resonance and the short-wavelength radio frequency has been used as the wireless energy transfer scheme.
The wireless power transmission system includes a transmitter and a receiver. The transmitter wirelessly transmits power to the receiver, and the receiver receives the power from the transmitter and performs the operation according to the reception of the power.
In this case, since the transmitter cannot recognize the operating state of the receiver, the transmitter continuously transmits power to the receiver so that the receiver can normally operate always.
However, the transmitter always transmits the power to the receiver regardless of the operating state of the receiver as described above, so that high voltage is applied to the coil of the transmitter. Accordingly, when power is transmitted to the receiver thereafter, the erroneous operation or the breakage of the transmitter may occur. In addition, since the transmitter transmits the predetermined quantity of power to the receiver regardless of the quantity of power required by the load of the receiver, remaining power except for the power used in the load of the receiver may be wasted.